Diverse electronic relays to protect motors that have intensity transformers are known, such as in the case of U.S. Pat. No. 4,345,288 and French Pat. No. A-2,584,877. The use of these transformers has the inconvenience that said elements take up a lot of space, are very heavy and expensive. Other inconveniences of these conventional relays are: the high temperatures that they are subjected to cause rapid wear of the same; their incapacity to endure overloads or short-circuits; their easy inconsistency regarding the initially established parameters; their incapacity to operate correctly in the presence of high voltage interference; lack of suitable control of the tigerring parameters; difficulty or trouble in resetting the same; or lack of suitable protection in the corresponding circuits.
Besides the cited U.S. and French patents have the inconvenience that the transformers are too big and provide a very weak signal, therefore, it must be amplified in an amplification stage, which is vulnerable to possible interferences of any type (Rf, etc.); which determines that the relay can be triggered for reasons others than malfunctioning of the motor, which represents a serious inconvenience.
On the other hand, the known technology for making pick-ups refers to the conversion of intensity into voltage, mainly using resistive pickup, inductive pickup and by means of the cited transformers.
I resistive pickup, the intensity to be controlled passes through a resistor, generating a one-phase voltage in the terminals of the same.
In inductive pickup a coil without a ferromagnetic core (with the winding in the open), is used with magnetic permeability near the unit and without an appreciable magnetic gain.
In pickup by means of transformers three transformers and the resulting secondary intensity subsequently converts into one-phase voltage by means of any of the two above cited methods.
These three pickup methods have inconveniences such as the impossibility of allowing a suitable miniaturization, excessive generation of heat, scarce range of usage intensities, need of ferromagnetic shielding, need to amplify the signals upon providing weak signals, etc.
In order to achieve the aims and to overcome the above cited inconveniences, the invention consists of an electronic relay to protect motors and thyristors against symmetric overload, phase unbalance and short-circuit that has precise and reliabel adjustment of the triggering parameters, suitable indicators and protection systems, and a simple and easy reset procedure. Besides, the present invention does not use intensity transformers thus its cost is advantageously low and its size is advantageously small.
The electronic relay of the invention, in its triggering function due to symmetric overload, generates some one-phase signals by means of three coils or pickups.
Each one of the three pickups is comprised by a U-shaped frame with one of its vertical branches longer than the other one for fastening thereof to the printed circuit. Between the vertical branches of the frame there is a core upon which the coil itself is placed, which is determined by a high number of spirals. In this way, free space between the coil and the frame is determined.
Each one of the three cables, through which the motor is fed, are made to pass through the free space comprised between the frame and a pickup coil, so that the passing of intensity generates a variable magnetic field generated upon the passing of the current, which is led through the core, generating at the outlet of the coil, a high voltage, that is proportional to the consumed intensity.
This arrangement solves the problems posed above, since the use of amplifying covers is no longer needed, nor is heat generated, nor is ferromagnetic shielding needed; which is a big advantage.
Besides, the pickups can be made of a minimal size, just as it will be commented on hereinafter; which likewise constitutes a big advantage.
The signals provided by the pickups are rectified by means of three diodes, filtered by two capacitors and the voltage thereof limited by a zener diode. Thus, a continuous voltage proportional to the motor line intensity is obtained. The level of said voltage is preset by means of an octuple microswitch which permits the variation of the total resistance of a group of eight resistors connected in shunt between said voltage and mass.
When this continuous voltage is equal to a reference voltage provided by a resistive divider connected in the inverting input of an operational amplifier, adjustment of the nominal intensity of the triggering of the relay is achieved. This reference voltage keeps the output of the operational amplifier in logic state 0, as long as its non-inverting input does not reach the value of said reference voltage.
In this non-inverting input, the continuous voltage alluded to first of all is applied by means of a R-C network that can be timed in five scales and comprised of four resistors and a quadruple microswitch that permits the variation of the feed resistence of the corresponding capacitor connected by means of a resistor fixed to the non-inverting input of the operational amplifier. When said input reaches the pre-set level of the reference voltage of the inverting input, the output of the operational amplifier for logic state 1, sending a positive signal through a diode and a resistor to the gate of a thyristor; whereby the latter enters in conduction and depolarizes by means of a resistor the base of a transistor. This makes said transistor go from saturation to blocking, with which the corresponding coil of a relay connected to the collector of the transistor deexcites, causing the relay to remain in the triggered state with two of its contacts closed and the other two open. Thus, the motor to be protected conveniently connected to said contacts, disconnects upon the coil of its contactor deexciting. This situation is indicated since a lighted indicator, connected through a resistor to the collector of the above cited transistor, receives in these circumstances the voltage needed for its activation.
In the electronic relay of the invention, in its triggering function due to phase unbalance, the one-phase signals generated by the above cited coils, are rectified by three other diodes and filtered respectively by both pairs of resistors and capacitors. These three filtered signals are applied respectively to the inverting inputs of three other operational amplifiers. On the other hand, said inputs receive a positive polarization by means of respective resistors connected to a positive voltage, thus guaranteeing a logic state equal to 0 in the outputs of said operational amplifiers during the absence of one-phase signals due to a dead motor.
The non-inverting inputs of these three operational amplifiers are polarized by a resistive divider at half the continuous voltage that was alluded to in paragraph two of this part. In this way, if the phases are balanced, the inverting inputs of said operational amplifiers are polarized with a level double that of the non-inverting ones, with which the outputs of these operational amplifiers remain in the logic state 0. If a reduction of any of the one-phase signals is produced below half the continuous voltage level alluded to in paragraph two of this part, any of the three operational amplifiers affected by this phase defect, will put its output in logic state 1.
The outputs of these three operational amplifiers connect through the corresponding diodes with the same electric point that connects with the diode of the output of the operational amplifier alluded to in paragraph three of this part, therefore any logic state 1 in the outputs of the three operational amplifiers will send a positive to the gate of the thyristor, which will enter into conduction, repeating the above cited process, whereby the motor to be protected will disconnect and the lighted indicator will become activated.
The electronic relay of the invention has triggering due to short-circuit, for which purpose a resistive divider that injects the continuous voltage alluded to in paragraph two of this part to the base of a transistor. Some of the resistors of this resistive divider can be connected or disconnected by means of another quadruple microswitch, which permits the level of triggering intensity due to short-circuit to be adjusted. The base of the transistor allueded to also connects to a capacitor that protects it against high frequency interferences. While the base-emitter voltage of said transistor does not reach a specific level, the latter remains blocked, permitting another transistor, whose base connects to the collector of the previous one and that is fed by means of a resistor, it is in saturation and has a practically non-existent collector-emitter voltage, with which the cathode of a diode connected to the collector of this latter transister, has a logic level 0. Said cathode connects with the gate of the thyristor alluded to above in this section, therefore under these conditions, said logic level 0 will not lead the thyristor to conduction, so the relay is not triggered due to short-circuit.
However, if said logic level reaches the value 1, the thyristor will enter in conduction, just as it happened when the output of any of the operational amplifiers had a logic level 1, and the relay will be triggered due to short-circuit. This happens when due to a short-circuit the continuous voltage alluded to in paragraph two of this part increases until it exceeds the blocking base-emitter voltage of the transistor alluded to first of all in the above paragraph, whereby said transistor passes to conduction, practically cancelling the base-emitter voltage of the following transistor, which will pass to blocking, and the feed voltage will be injected, through a resistor and diode connected to the collector of this last transistor, at the gate of the thyristor, which is equal to a logic level 1 in said gate which leads the thyristor to conduction and at which the triggering of the relay due to short-circuit is produced.
Resetting the relay is done simply by pushing a reset button which leads the gate of the thyristor to ground thereby cancelling its voltage and blocking it. At the same time the transistor enters saturation upon its base polarizing by means of a resistive divider, thus the relay coil is excited again, the lighted indicator is deactivated and the relay contacts that were closed open, while those that were open close.
The device of the invention also has a test button. Upon pushing said button, with the motor to be protected started in any charge state, the one-phase signal of one of the three coils alluded to in paragraph two of this part is short-circuited with ground, thus a phase fault is simulated and the relay is triggered by means of the the same process commented on above. This allows one to check when desired whether the operation due to phase unbalance is correct.
In the present invention a feed source comprised of a one-phase transformer, followed by a rectifying bridge and filter condensers whose output is applied to a regulator that supplies a stabilized voltage, has been provided for. When this voltage is applied to the electronic relay circuit, another visual indicator of said circuit remains lighted.
Besides, the electronic circuit relay has different protection and safety elements. Thus, the relay coil has a shunt connected diode that protects the transistor against disconnection surge of said coil. On the other hand the important voltage points in the device are protected, by means of capacitors, against transitory high frequency surges. These surges can also cause untimely triggerings in the operational amplifiers, therefore a R-C network has been included in the output of the same that provides suitable protection by means of a small that provides suitable protection by means of a small delay. Before said R-C network, the operational amplifier outputs include both diodes that were already mentioned in this part. These diodes protect their respective outputs against short-circuits between the same by direct connection to different logic states.
In terms of the amperage or range of intensities, different pickups have been designed with variations of the dimensions, number of wound rings, the size of the cores, the size and shape of the frames, the holes for passing the conductors, etc. Hence, novel features are obtained such as a great miniaturization of the components, achieving for example a miniature relay of up to 40 amperes with some exterior dimensions of 93.times.76.times.45 mm. Another novel feature is that a pickup system with a passing conductor that makes the installation and connection work easier is obtained, also providing the system with great safety. A wide range of nominal intensities, from 4 A. up to 180 A is obtained and with a passing conductor, which has not been achieved with other pickup systems.
With respect to known pickup technologies, the advantages of this novel inductive pickup method with ferromagnetic cores in the coils are the following:
With regard to resistive pickup technology:
Galvanic separation between the line of the motor and the relay PA1 Total immunity with regard to short-circuits and overloads. PA1 Heat generation free pickup PA1 Much broader range of usage intensities. In this case, 15 A are not normally exceeded. PA1 Voltage generated not affected by temperature. Less thermal drift PA1 Total immunity with regard to perturbation magnetic fields PA1 Ferromagnetic shielding outside the relay is not required PA1 Without electronic amplifier of the voltages generated, for practical use thereof in the circuit PA1 More sensitive pickup, in this case it is not possible to go below 20 or 30 amperes PA1 The 2nd. intensity conversion stage is avoided PA1 3 transformers up to 180 are made unnecessary PA1 The rest of the advantages indicated above.
With regard to inductive pickup with coil without a ferromagnetic core:
Connection strips to the line of the motor are not necessary to maintain the distance between the horizontal axis of the conductor and the coil. A variation of the same gives rise to important variations of the generated voltage.
With regard to technology based on intensity transf-formers:
Hereinafter, to provide a better understanding of this specification and forming an integral part of the same, some figures in which the object of the invention has been represented in an illustrative and non-restrictive manner are attached hereto.